The present disclosure relates generally to apparatuses and methods of screening and selecting leaflets for use in prosthetic heart valves. More particularly, it relates to apparatuses and methods for droop testing leaflets that measures flexural stiffness of the tissue in order to screen leaflets for use in prosthetic heart valves, for example prosthetic aortic transcatheter valves (TCV).
Prosthetic heart valve fabrication, including aortic transcatheter valve (TCV) fabrication, requires leaflets and skirts to be cut in predetermined geometry from animal-derivative tissue (e.g., porcine pericardium) and then sewn together, often as a tri-leaflet valve. Durability and leaflet wear are critical factors in maintaining acceptable performance over the lifetime of the device. A large factor in the durability of a prosthetic tissue heart valve is the processing and selection of the material. For example, there are three main criteria used to select areas of a pericardial sheet used for the leaflets: thickness, stiffness, and surface features. There are existing technologies to perform thickness mapping. There are also existing technologies to measure material extensibility in terms of deflection (along a Z-axis) in response to an applied load. There is a need for technology to evaluate material stiffness in a non-destructive method. There have been studies which indicate good correlation existing between leaflet droop and material extension in response to applied load.
Material extensibility has shown some indications towards affecting leaflet dynamics and stretching over long duration in wear testing. When a leaflet is suspended from a pin or a forceps, it has a tendency to droop in response to gravity. A leaflet having less stiffness is less resistant to drooping/bending forces, and a leaflet having greater stiffness and higher flexural rigidity is more resistant to drooping/bending. Studies have been conducted to correlate the amount of droop to mechanical properties of the material and which correlates well to a percentage strain at physiological loading. The material property (mechanical properties such as UTS, percentage strain, Young's Modulus) of pericardial tissue, for example, is highly variable and non-uniform within the sac. Valves constructed with stiff leaflets combined with droopy leaflets can cause asynchronous valve closure causing regurgitant fractions to increase. With quantitative measurements, leaflets can be matched or classified based on their droop values.
In light of the above, there is a need for a sensitive, reliable, and repeatable measurement apparatus and method to evaluate leaflet droop in a quantitative manner in order to screen leaflets.